Mobile network control device and mobile network control method

ABSTRACT

A mobile network control apparatus capable of improving transmission efficiency without giving any processing loads to nodes of a mobile network. In mobile routers  121, 131, 132  to which the present apparatus is applied, a tunnel failure detection unit  204  detects a failure of packet tunneling executed using an interface  205 - 1  of the mobile routers  121, 131, 132.  A multi-homing detection unit  202  searches for interfaces  205 -A,  205 -B having a connection route to a global network  101  out of an interface  205  of the mobile routers  121, 131, 132  according to the detected failure of packet tunneling. A bidirectional tunneling unit  203  executes packet tunneling using the searched interfaces  205 -A,  205 -B instead of the interface  205 - 1.

TECHNICAL FIELD

The present invention relates to a mobile network control apparatus anda mobile network control method, and more particularly, to a mobilenetwork control apparatus having a plurality of connection routes to aglobal data communication network (hereinafter referred to as “globalnetwork”) and a mobile network control method therefor.

BACKGROUND ART

The Internet today has evolved into a stage at which many datacommunication networks (hereinafter referred to as “network”) aredeployed around a system of fixed network node. These peripheralnetworks are known as edge networks, while the fixed network node systemsurrounded by the edge networks is known as a core network. With theemergence and development of wireless technologies, these edge networksare further used for wireless solutions. For example, as described in“Network Mobility Support Terminology” (Ernst, T., and Lach, H.,Internet Draft: draft-ernst-nemo-terminology-01.txt, October 2002, Workin Progress) and “Network Mobility Support Requirements” (Ernst, T., andLach, H., Internet Draft: draft-ernst-nemo-requirements-00.txt, October2002, Work in Progress), a special edge network called a “mobilenetwork”, that is, a moving network is being formed.

The mobile network is a network of a node at which the entire networkchanges its attachment points to the global network such as the Internetand usually requires a mobile router (device bridging the mobile networkto the global network) within the mobile network between differentaccess routers (actually, the access routers themselves may be mobile).For example, the mobile network includes a network attached to people(known as a personal area network, or PAN) and a network of sensorsdeployed in a vehicle such as car, train, ship or airplane. For a masstransport system such as airplane, train or bus, it is possible toprovide passengers with onboard Internet access so as to connect aremote host using a laptop, personal digital assistance (PDA) orcarphone. Individual nodes within such a mobile network are usuallyconnected to a central apparatus (that is, mobile router), and when anetwork is in motion, the individual nodes do not change theirattachment points and the mobile router changes the attachment points sothat the entire network moves instead.

Therefore, the problem with the network in motion is different from theproblem with conventional mobility support addressed by Mobile IPv4 (see“IP Mobility Support”, Perkins, C. E. et. al., IETF RCF 2002, October1996) in IPv4 (see “Internet Protocol”, DARPA, IETF RFC 791, September1981) and Mobile IPv6 (“Mobility Support in IPv6”, Internet Draft:draft-ietf-mobileip-ipv6-18.txt, Work in Progress, June 2002) in IPv6(“Internet Protocol Version 6 (IPv6) Specification”, Deering, S., andHinden, R., IETF RCF 2460, December 1998). A main objective of MobileIPv4 and Mobile IPv6 is to provide mobility support to individual hostsrather than the entire network.

In a mobile IP, each mobile node has a unique home domain. When a mobilenode is attached to its home network, a unique global address known as ahome address is assigned to the mobile node. On the other hand, when amobile node is away, that is, attached to some other foreign networks, atemporary global address known as a care-of-address is assigned to themobile node. The idea of mobility support is to make it possible toreach the mobile node by referencing the home domain even when themobile node is attached to other foreign networks. This is achieved byintroducing an entity (home agent) to the home network.

The mobile node registers care-of-addresses with the home agent using amessage known as “binding update.” The home agent is responsible forintercepting a message addressed to the home address of the mobile node.Also, the home agent is responsible for forwarding the packet to thecare-of-address of the mobile node using IP-in-IP tunneling (see“IP-in-IP Tunneling”, Simpson, W., IETF RFC 1853, October 1995 and“Generic Packet Tunneling in IPv6”, Conta, A., and Deering, S., IETF RFC2473, December 1998). The IP-in-IP tunneling involves encapsulating anoriginal IP packet with another packet. The original packet may also becalled “inner packet” and the new packet which encapsulates the innerpacket may also be called “outer packet.”

When the concept of mobility support for individual hosts is extended tomobility support for a network of nodes, the objective of solving theproblem of the mobile network is to make it possible to reach nodeswithin the mobile network using unique addresses no matter where on theInternet the mobile network is attached to. Several attempts have beenmade so far to provide a network mobility support. Most of them use abidirectional tunnel between a mobile router and a home agent of themobile router (see “Mobile Router Tunneling Protocol”, Kniveton, T., et.al., Internet Draft: draft-kniveton-mobrtr-03.txt, Work in Progress,November 2002, “Issues in Designing Mobile IPv6 Network Mobility withthe MR-HA Bidirectional Tunnel (MRHA)”, Internet-Draft:draft-petrescu-nemo-mrha-00.txt, Work in Progress, October 2002, “IPv6Reverse Routing Header and Its Application to Mobile Networks”, Thubert,P., and Molteni, M., Internet Draft:draft-thubert-nemo-reverse-routing-header-01.txt, Work in Progress,October 2002, and “Mobile Networks Support in Mobile IPv6 (Prefix ScopeBinding Updates)”, Ernst, T., Castelluccia, C., Bellier, L., Lach, H.,and Olivereau, A., Internet Draft:draft-ernst-mobileip-v6-network-03.txt, March 2002).

In a bidirectional tunnel between the mobile router and home agent, whenin a home domain, the mobile router which controls the mobile networkperforms routing of packets on the mobile network using several routingprotocols. On the other hand, when the mobile router and its networkmove to a foreign network, the mobile router registers thecare-of-address with the home agent. Then, an IP-in-IP tunnel is set upbetween the mobile router and home agent. The mobile router uses therouting protocol used when it existed in the home domain on the IP-in-IPtunnel as well. This means that all packets directed to the mobilenetwork are intercepted by the home agent and forwarded to the mobilerouter through the IP-in-IP tunnel. Then, the mobile router forwards thepacket to a host in the mobile network. Furthermore, when the node inthe mobile network wishes to send a packet to the outside of thenetwork, the mobile router intercepts the packet, forwards the packet tothe home agent through the IP-in-IP tunnel and then the home agent sendsthe packet to an intended recipient (packet destination set by the nodewithin the mobile network).

However, the above described simple approach of the bidirectional tunnelcannot satisfy requirements of other powerful features (e.g.,multi-homing) of IPv4 and IPv6 sufficiently. When there is a pluralityof egress interfaces which offer independent routes to the globalnetwork, the mobile network can be multi-homed. When all theseinterfaces belong to the same router, only the router is multi-homed.The nodes of the mobile network which exist behind the router can onlysee one egress router and are not multi-homed. On the other hand, whenthese interfaces belong to different routers, the nodes of the mobilenetwork see a plurality of egress routers and are therefore multi-homed.

The mobile network typically has wireless connection to the globalnetwork. In recent years, wireless technologies have made significantprogress, but they could cause problems of instability of channels andnoise, compared to wired networks. One of the advantages of multi-homingis the ability of a network node to use an alternative route to reachand be reached by the global network even when a certain uplink goesdown.

However, according to the bidirectional tunnel mechanism used by themobile router, nodes can only select one router as a default router.When this router loses its connection to the global network, the routercannot maintain the tunnel with the home agent. Moreover, a node usingthis router loses its connectivity to the global network even whenanother mobile router having an active link with the global networkexists on the same network. Then, the nodes of the mobile network soonrecognize that the default router has lost the route to the globalnetwork and selects an alternate mobile router as a default router.

Such a scheme depends on the nodes of the mobile network discoveringroutes for themselves, giving processing loads to the nodes having verylimited processing capacity, e.g. embedded devices. Furthermore, thereis a possibility that a delay may be produced for the nodes to recognizethat the current default route has gone down. Moreover, different mobilerouters broadcast prefixes of different subnets, and therefore when themobile nodes eventually switch default routers, it is necessary to usedifferent care-of-addresses and send a binding update to the home agent,which may further increase the delay in discovering routes.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a mobile networkcontrol apparatus and mobile network control method capable of improvingthe transmission efficiency without giving any processing burden tonodes of a mobile network.

The mobile network control apparatus according to an aspect of thepresent invention is a mobile network control apparatus, which maintainsa connection that is constructed between a node belonging to a mobilenetwork and a global network and is constructed through a routerapparatus that has an interface having a connection route to the globalnetwork and belongs to the mobile network, and the mobile networkcontrol apparatus comprises: a detector section that detects a failureof packet tunneling executed using a first interface of the routerapparatus; a search section that searches for a second interface of therouter apparatus according to the detected failure of the packettunneling; and an execution section that executes packet tunneling usingthe searched second interface instead of the first interface.

The mobile network control method according to another aspect of thepresent invention is a mobile network control method, which maintains aconnection that is constructed between a node belonging to a mobilenetwork and a global network and is constructed through a routerapparatus that has an interface having a connection route to the globalnetwork and belongs to the mobile network, and the mobile networkcontrol method comprises: a detection step of detecting a failure ofpacket tunneling executed using a first interface of the routerapparatus; a search step of searching for a second interface of therouter apparatus according to the failure of the packet tunnelingdetected in the detection step; and an execution step of executingpacket tunneling using the second interface searched in the search stepinstead of the first interface.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a general communication networksystem having mobile routers to which a mobile network control apparatusaccording to an embodiment of the present invention is applied;

FIG. 2 is a block diagram showing the internal configuration of themobile router;

FIG. 3 is a flow chart illustrating an operation example of the mobilerouter;

FIG. 4A is a flow chart illustrating another operation example of themobile router; and

FIG. 4B is a flow chart illustrating the continuation of the operationexample shown in FIG. 4A.

BEST MODE FOR CARRYING OUT THE INVENTION

In order to solve the above described problems, the present inventionallows a mobile router to which a mobile network control apparatus isapplied to use an alternative router instead. This involves the mobilerouter detecting the presence of another mobile router in a networksegment of an ingress interface having an independent route to a globalnetwork. When an egress link of the mobile router is disconnected, themobile router acquires a care-of-address from another mobile router,sends a binding update to a home agent and reconstructs a bidirectionaltunnel which passes through another mobile router. Likewise, the mobilerouter having a plurality of egress interfaces can also switch betweenegress interfaces when maintaining the bidirectional tunnel. Thiseliminates the necessity of the nodes of the mobile network to changethe default router. Actually, the nodes of the mobile network need notrecognize the fact that the mobile router has changed the alternativeroute to the global network. Thus, all extra processing loads andlatency associated with the nodes of the mobile network which performsdefault router switching and updating care-of-address bindings areeliminated, which can consequently improve the transmission efficiency.

The present invention relates to a mobile router which roams within aglobal network and is intended to maintain connectivity between a nodeconnected to an ingress interface of the mobile router and its homeagent through a bidirectional tunnel. The mobile router needs to inspectinformation passively entering the ingress interface and detect whetherthere are any other mobile routers which broadcast an alternative routeto the global network. When such mobile routers are detected, the mobilerouter which has performed the detection reconstructs a bidirectionaltunnel with the home agent through the above described alternative routeevery time the egress interface fails. Furthermore, the mobile routeritself may be multi-homed. In this case, when the primary egressinterface of the bidirectional tunnel fails, the mobile router isallowed to switch between the egress interfaces.

An apparatus and method for providing a roaming network (mobile network)with global connectivity will be disclosed below. To help understand thedisclosed invention, the following definitions are used:

A “packet” is a self-contained unit of data having any possible formatthat can be delivered on a data network. The packet normally consists oftwo parts; a header and a payload. The payload contains data to betransmitted and the header contains information to assist transmissionof the packet. The header contains a source address and destinationaddress to identify the sender and receiver of the packet.

“Packet tunneling” refers to a self-contained type packet beingencapsulated into another packet. The operation of packet tunneling isalso called “packet encapsulation.” Furthermore, a packet that is beingencapsulated is called “tunneled packet” or “inner packet”, and a packetthat encapsulates the inner packet is called “tunneling packet” or“outer packet.” The entire inner packet forms a payload of the outerpacket.

A “default router” of a network element, refers to a router to which allpackets sent by the network element without being aware of otherconnection routes up to a destination are delivered and which resides onthe same link as the network element.

A “mobile node” is a network element which changes attachment points tothe global network. For example, the “mobile node” refers to an end-userterminal, or an intermediate network element which serves as a gateway,router or intelligent network hub which can change its attachment pointsto the global network. The mobile node which is an enduser terminal ismore specifically called a “mobile host”, while the mobile node which isan intermediate network element is more specifically called a “mobilerouter.”

A “home address” is a primary global address assigned to the mobile nodeand is used to enable the mobile node to be reached regardless of whereon the global network the mobile node is attached to.

A mobile node which is attached to the global network at a point atwhich the home address has topological compatibility with an addressused in the vicinity of the attachment point is said to be “at home.”The vicinity of the attachment point which is controlled by a singleadministrative authority is called a “home domain” of the mobile node.

A mobile node which is attached to the global network at a point atwhich the home address has no topological compatibility with an addressused in the vicinity of the attachment point is said to be “away.” Thevicinity of the attachment point is called a “foreign domain.”

A “care-of-address” is a temporary global address assigned to a mobilenode that is away and the care-of-address assigned has topologicalcompatibility with the address used in the vicinity of the attachmentpoint to the global network.

A “home agent” is a network entity which exists in the home domain ofthe mobile node, provides a service of registering the care-of-addressof the mobile node when the mobile node is away so as to forward apacket directed to the home address of the mobile node to thecare-of-address of the mobile node.

A “binding update” is a message sent from the mobile node to the homeagent or a correspondent node and notifies the recipient (home agent orcorrespondent node) of the current care-of-address of the sender (mobilenode). In this way, a “binding” is formed between the care-of-address ofthe mobile node and the home address at the recipient.

With reference now to the attached drawings, embodiments of the presentinvention will be explained in detail below.

In the following descriptions, specific numbers, times, structure andother parameters are used in explanations to help understand the presentinvention thoroughly, but it is apparent for those skilled in the artthat the present invention can be implemented without such specificdetails.

FIG. 1 is a configuration diagram of a typical communication networksystem having mobile routers to which a mobile network control apparatusaccording to an embodiment of the present invention is applied. In thecommunication network system shown in FIG. 1, the operations of twomulti-homed mobile networks 102, 103 connected to a global network 101are optimized.

In FIG. 1, a mobile router 121 of the mobile network 102 has two egressinterfaces connected to the global network 101 through two access points111, 112 of the global network 101, and therefore the mobile network 102is multi-homed. Furthermore, the mobile network 103 is also linked tothe global network 101 through an egress interface linked to the mobilenetwork 102 and also connected to the global network 101 through anegress interface connected to an access point 113 of the global network101, and therefore the mobile network 103 is also multi-homed.

Both the mobile networks 102 and 103 are multi-homed but there is adifference therebetween. Since a mobile router 131 does not broadcastthe fact that the mobile router 131 itself has a connection route(hereinafter referred to as “global connection”) to the global network101, only one default router, that is, the mobile router 121 is seenfrom the mobile node 122 within the mobile network 102. On the otherhand, two default routers, that is, the mobile routers 131, 132 are seenfrom the mobile nodes 133, 134 within the mobile network 103.

As shown above, different types of multi-homed mobile networks areillustrated, and thus the present invention can be completely disclosed.

The mobile routers 121, 131, 132 shown in FIG. 1 have similar internalconfigurations. FIG. 2 is a block diagram showing the internalconfiguration of the mobile routers 121, 131, 132.

The mobile routers 121, 131, 132 include an upper layer section 201, amulti-homing detection unit 202, a bidirectional tunneling unit 203, atunnel failure detection unit 204 and a single or a plurality of (e.g.,N) network interfaces (hereinafter referred to as “interfaces”) 205-1,205-2, . . . , 205-N. Hereinafter, an arbitrary one of the interfaces205-1 to 205-N will be simply referred to as an interface 205.

The upper layer section 201 is a block symbolizing an actual protocolstack that handles network protocols such as IPv4 and IPv6 and allprotocols above these network protocols and encapsulates all protocolsrelated to inter-terminal connections. Likewise, the interfaces 205-1 to205-N are blocks symbolizing physical network interface cards having allnecessary drivers and protocol stacks necessary to drive the physicalnetwork interface cards.

Interfaces (e.g., interfaces 205-1 to 205-N) generally include one ormore interfaces used as egress interfaces and one or more interfacesused as ingress interfaces. The ingress interface is connected tonetwork elements (e.g., mobile nodes 122, 133, 134) on local networks(e.g., mobile networks 102, 103) and the egress interface is connectedto a global network (e.g., global network 101).

Here, the intermediate functionality inserted between the networkprotocol layer and network interface layer (that is, functionalities ofthe multi-homing detection unit 202, bidirectional tunneling unit 203and tunnel failure detection unit 204) will be explained in detail.

The multi-homing detection unit 202 detects whether another router thatbroadcasts the availability of a route to the global network exists onthe same link as one of the ingress links. This detection is realized byinspecting all packets entering from the interface 205 through a packetflow path 216. These packets are handed over to the upper layer section201 to be subjected to normal processing through a packet flow path 211.Furthermore, the multi-homing detection unit 202 can also detect whetherthe mobile routers 121, 131, 132 themselves are multi-homed or not bydeciding whether a plurality of active egress interfaces exists in theinterfaces 205-1 to 205-N through a signal flow path 219.

The bidirectional tunneling unit 203 carries out bidirectional packettunneling for incoming packets and outgoing packets. All packets sentfrom a packet flow path 212 are encapsulated and forwarded to the homeagent. The upper layer section 201 is expected to only switch betweenoutgoing packets directed to the global network 101 via the packet flowpath 212. For a packet that is destined to one of the ingress links, theupper layer section 201 can also directly switch between packets to anappropriate interface 205 using a packet flow path 213. Afterencapsulation, the outgoing packet will be routed to the appropriateinterface 205 to be sent out.

The bidirectional tunneling unit 203 decapsulates an incoming packetwhich has been encapsulated in a tunnel. The decapsulated packet ishanded over to the upper layer section 201 via the packet flow path 212for normal processing.

The tunnel failure detection unit 204 detects disconnection of a linkthrough which the bidirectional tunneling goes, that is, the failure ofbidirectional packet tunneling through a signal flow path 218. Tunnelfailures can occur when the home agent has no capacity to receive anytunnel packets. Such tunnel failure occurs may be indicated by theinterface 205 or by a consistent rejection of packets by an intermediaterouter. Generally, most wired or wireless interfaces including theinterface 205 provide a system call to query the link status of aphysical channel. The tunnel failure detection unit 204 can detect thedisconnection of the link through such a system call.

Furthermore, when an intermediate network node cannot forward a packetto the next (intermediate) destination for some reason, most networkprotocols provide means for feedback to notify the sender of thisfailure. Again, the tunnel failure detection unit 204 captures suchnotification, and determines that the tunnel has failed afterconsistently receiving such notification for an extended period of time.When the failure is detected, this becomes a trigger and thebidirectional tunneling unit 203 takes appropriate action using thesignal flow path 215.

The applicability of the present invention greatly depends on thedetection/discovery of another router having an alternative route to theglobal network 101 (hereinafter the router having an alternative routeto the global network 101 will be referred to as “alternative router”).Therefore, the multi-homing detection unit 202 plays a very importantrole here. In order to detect the presence of other alternative routers,the multi-homing detection unit 202 inspects all incoming packets anddetects packets including an advertisement message sent from otherrouters.

According to most network protocols used in a packet-switched network,the router periodically (for example) broadcasts an advertisementmessage including information on the router to all nodes on the samelink. From these messages, the recipient node can know whether therouter has a path to the global network or not. For example, in IPv6neighbor discovery described in “Neighbor Discovery for IP Version 6”(Narten, T., Nordmark, E., and Simpson, W., IETF RFC 2461, December1998), when the router sends an advertisement message to a node on theingress link, the router sets a router lifetime field to a non-zerovalue and then sends the advertisement message. Thus, for thebroadcasted lifetime, it is possible to indicate that the router isavailable as a default router (that is, a router having a connectionroute to the global network). Therefore, when the multi-homing detectionunit 202 on the mobile router 121, 131, 132 is implemented in an IPv6environment, it is possible to detect the presence of other alternativerouters using this. Once an alternative router is detected, thealternative router can be added to a list of alternative routers storedby the multi-homing detection unit 202.

Furthermore, the mobile router 121, 131, 132 also has a possibility ofhaving a plurality of active egress interfaces simultaneously, in otherwords, a possibility that the mobile router itself is multi-homed. Thisis detected by the multi-homing detection unit 202. However, thispresupposes that one of the egress interfaces is a primary egressinterface used by all packets sent from the local network. Furthermore,the egress interface is also a normal egress interface through which abidirectional tunnel passes.

In this case, other active egress interfaces are classified asalternative egress interfaces and stored in a list of alternative egressinterfaces stored by the multi-homing detection unit 202. Furthermore,the multi-homing detection unit 202 monitors the interfaces 205-1 to205-N continuously, and therefore when an egress interface which is nomore active is detected, it is also possible to remove such an egressinterface from the list of alternative egress interfaces.

Next, the operation of the mobile router 121, 131, 132 will beexplained. The present invention will be generalized by describing acase where an egress interface goes down in a mobile router (e.g.,mobile router 132) which is not multi-homed in the first part of thefollowing disclosure and a case where an egress interface goes down in amulti-homed mobile router (e.g., mobile router 121) in the later part ofthe disclosure.

Under normal operation, the bidirectional tunneling unit 203 uses aprimary egress interface for transmitting a tunnel packet. When thetunnel failure detection unit 204 detects failures of tunneling whichpasses through the primary egress interface, the tunnel failuredetection unit 204 has to construct an alternative connection route forpacket tunneling. In the following explanations, suppose the interface205-1 is the egress interface used for the failed tunneling.

First, the operation of the mobile router 132 which is not multi-homedwill be explained with reference to FIG. 3.

After the tunnel failure detection unit 204 detects the failure of thebidirectional tunneling using the interface 205-1 (S1010), themulti-homing detection unit 202 conducts a check to acquire a router inthe list of alternative routers and thereby decides the presence/absenceof a router for global connection (S1020). When the result of thisdecision shows that the router having global connection is included inthe list of alternative routers (S1020: YES), the multi-homing detectionunit 202 selects the router in the list and moves to step S1030. When norouter having global connection exists, that is, the list of alternativerouters is empty (S1020: NO), the mobile router 132 has to enter adisconnected state (S1040). In the disconnected state, the mobile router132 may have to discard all packets to be forwarded to the globalnetwork 101 and passively wait for the egress link to be restored, andtherefore the process moves to step S1110.

In step S1030, it is decided whether the care-of-address need beacquired from the selected router or not. For example, when the currentaddress of the ingress interface for the link in which the selectedrouter exists, in other words, the ingress interface having a connectionroute to the selected router (referred to as “interface 205-A” in thisembodiment) is not a valid global address (e.g., when the currentaddress is a private address), the care-of-address needs to be acquired(assigned) from the selected router (S1030: YES), and therefore thecare-of-address is acquired from the selected router (S1050). On theother hand, when the current address is a valid global address, thecare-of-address need not be acquired from the selected router (S1030:NO), and therefore the process skips steps S1050, S1060 and moves tostep S1070.

When the multi-homing detection unit 202 discovers a new alternativerouter, it may also immediately acquire the care-of-address from thealternative router. In this case, the discovered care-of-address of thealternative router is stored in the list of alternative routers togetherwith the alternative router entry. By so doing, it is possible toeliminate the necessity for acquiring the care-of-address in step S1050after selecting the router in step S1020.

Then, in step S1060, it is decided whether the acquisition of thecare-of-address in step S1050 has been successful or not. When theacquisition of the care-of-address is successful (S1060: YES), theprocess moves to step S1070, whereas when the acquisition of thecare-of-address is not successful (S1060: NO), the process moves to stepS1100.

In step S1070, a binding update is sent to the home agent through theselected router. This binding update is sent so that the mobile router132 notifies the home agent that the start address of the bidirectionaltunnel is changed to the address of the interface 205-A. Then, thesystem waits for reception of an acknowledgement (ACK) of transmissionof the binding update.

In step S1080, it is decided whether the ACK has been received or not.When the ACK has been received (S1080: YES), this means that abidirectional tunnel with the home agent has been newly constructed as aprovisional measure. Then, the process moves to step S1090. On the otherhand, when a timeout results while the system is waiting for receptionof the ACK or when a negative acknowledgement (NACK) is received (S1080:NO), the process moves to step S1100.

In step S1090, the bidirectional tunneling unit 203 enables theinterface 205-A to be used as an interface which becomes the startingpoint (end point) of a bidirectional tunnel and also enables the globaladdress (care-of-address) associated with the link to the routerselected from the interface 205-A to be used as a new temporary sourceaddress (destination address) of the bidirectional tunnel. Then,bidirectional tunneling using the interface 205-A is performed. Theprocess then moves to step S1110.

In step S1100, the selected router is removed from the list. Since theselected router is removed from the list in this way, it is possible tocarry out maintenance of the list of alternative routers and moreefficiently perform similar alternative route search operation swhichwill be executed later. After executing step S1100, the process returnsto step S1020.

In step S1110, the tunnel failure detection unit 204 monitors thedisconnected link, that is, the link between the interface 205-1 andglobal network 101. The tunnel failure detection unit 204 continues themonitoring until this link is restored and when this link is restored,the process moves to step S1120. In step S1120, the bidirectional tunnelconstructed as the provisional measure is canceled and bidirectionaltunneling using the interface 205-1 is restarted.

Though not shown in FIG. 3, the tunnel failure detection unit 204 alsomonitors failures of the bidirectional tunneling newly constructed asthe provisional measure. When a failure of this bidirectional tunnelingis detected, it is obvious that an operation similar to that shown inFIG. 3 is executed.

Furthermore, when the home agent approves that the mobile router 132registers a plurality of care-of-addresses simultaneously, it is alsopossible to further optimize the above described operation. Morespecifically, every time the multi-homing detection unit 202 discovers anew alternative router and acquires a care-of-address from thisalternative router, the multi-homing detection unit 202 immediatelysends a binding update for registering the acquired care-of-address asan alternative care-of-address to the home agent. In this case, it isnot necessary to request a care-of-address or send a binding updateafter the router is selected. Therefore, it is possible to simplifyprocessing during a period from the time the construction ofbidirectional tunneling becomes necessary as a provisional measure tothe time the bidirectional tunneling is actually constructed. Also, itis possible to shorten the required time.

Next, the operation of the multi-homed mobile router 121 will beexplained with reference to FIG. 4A and FIG. 4B.

After the tunnel failure detection unit 204 detects a failure of thebidirectional tunneling using the interface 205-1 (S1010), themulti-homing detection unit 202 conducts a check to acquire an egressinterface in the list of alternative egress interfaces and therebydecides the presence/absence of an active egress interface (S1011). Whenthe result of this decision shows that an active egress interface isincluded in the list of alternative egress interfaces (S1011: YES), themulti-homing detection unit 202 selects the egress interface(hereinafter referred to as “interface 205-B”) in the list and moves tostep S1012. When no active egress interface exists, that is, the list ofalternative egress interfaces is empty (S1011: NO), the process moves tostep S1020. That is, when the list of alternative egress interfaces isempty, the mobile router 121 continues executing an operation similar tothe above described operation of the mobile router 132 (S1020 to S1120).

In step S1012, a binding update is sent to the home agent through theselected interface 205-B. This binding update is sent so that the mobilerouter 121 connects the start address of the bidirectional tunnel to theaddress (care-of-address) of the interface 205-B. Then, the system waitsfor reception of an acknowledgement (ACK) of transmission of the bindingupdate.

Then, in step S1013, it is decided whether an ACK has been received ornot. When the ACK has been received (S1013: YES), this means that thebidirectional tunnel with the home agent has been newly constructed as aprovisional measure. Then, the process moves to step S1014. On the otherhand, when a timeout results while the system is waiting for receptionof the ACK or when a negative acknowledgement (NACK) is received (S1013:NO), the process moves to step S1015.

In step S1015, the selected interface 205-B is removed from the list.Thus, since the selected egress interface is removed from the list, itis possible to perform maintenance of the list of alternative egressinterfaces and more efficiently perform a similar alternative routesearch operation that will be executed later. After executing stepS1015, the process returns to step S1011.

On the other hand, in step S1014, the bidirectional tunneling unit 203enables the interface 205-B to be used for a provisional bidirectionaltunnel and executes bidirectional tunneling using the interface 205-B.Then, the process moves to step S1016.

In step S1016, the tunnel failure detection unit 204 monitors thedisconnected link, that is, the link between the interface 205-1 andglobal network 101. Then, the tunnel failure detection unit 204continues the monitoring until this link is restored and when this linkis restored, the process moves to step S1017. In step S1017, thebidirectional tunnel constructed as a provisional measure is canceledand bidirectional tunneling using the interface 205-1 is restarted.

Though not shown in FIG. 4A and FIG. 4B, the tunnel failure detectionunit 204 also monitors failures of the bidirectional tunneling newlyconstructed as the provisional measure. When a failure of bidirectionaltunneling is detected, it is obvious that operations similar to thoseshown in FIG. 4A and FIG. 4B are executed.

Furthermore, when the home agent approves that the mobile router 121registers a plurality of care-of-addresses simultaneously, the abovedescribed operation can be further optimized. More specifically, everytime the multi-homing detection unit 202 discovers a new alternativeegress interface, it immediately sends a binding update for registeringthe care-of-address as an alternative care-of-address to the home agent.In such a case, it is not necessary to request a care-of-address or senda binding update after the egress interface is selected. Therefore, itis possible to simplify processing during a period from the time theconstruction of bidirectional tunneling becomes necessary as aprovisional measure to the time the bidirectional tunneling is actuallyconstructed. Also, it is possible to shorten the required time.

The above described explanation of the mobile router 121 provided with aplurality of egress interfaces presupposes that the mobile router 121includes only a single bidirectional tunnel and uses only one of theplurality of egress interfaces as a primary egress interface. However,by providing the multi-homing detection unit 202, bidirectionaltunneling unit 203 and tunnel failure detection unit 204 to therespective egress interfaces used as the primary egress interfaces forthe bidirectional tunnel, it is possible to eliminate the abovedescribed presupposition and extend the present invention. In this case,the operation shown in FIG. 3 and the operations shown in FIG. 4A andFIG. 4B can be executed by the respective bidirectional tunnels.Especially, the multi-homing detection unit 202 related to a certain onebidirectional tunnel treats primary egress interfaces of the otherbidirectional tunnels as alternate egress interfaces. Then, tocompensate for the failure of bidirectional tunneling as required, it ispossible to use the other primary egress interfaces.

Thus, according to this embodiment, it is possible for the mobile routerusing bidirectional tunneling with the home agent to efficiently use themulti-homing technology used in the network protocol and minimizeadverse effects caused by the failure of the egress link. Using thepresent invention disclosed here, the mobile router can actively searchfor an alternative route to reconstruct a bidirectional tunnel with thehome agent, thereby eliminate the necessity for each mobile nodeattached to the mobile router to carry out processing of switchingdefault routers (this processing normally requires time) and minimizethe effects of disconnection caused by the failure of the link.

This application is based on the Japanese Patent Application No.2002-378457 filed on Dec. 26, 2002, the entire content of which isexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

The mobile network control apparatus and mobile network control methodaccording to the present invention have the effect of improvingtransmission efficiency without giving any processing loads to nodes ofa mobile network and are suitable for use as the mobile network controlapparatus having a plurality of connection routes with a global networkand a mobile network control method therefor.

1. A mobile network control apparatus, which maintains a connection thatis constructed between a node belonging to a mobile network and a globalnetwork and is constructed through a router apparatus that has aninterface having a connection route to said global network and belongsto said mobile network, the mobile network control apparatus comprising:a detection section that detects a failure of packet tunneling executedusing a first interface of said router apparatus; a search section thatsearches for a second interface of said router apparatus according tothe detected failure of the packet tunneling; and an execution sectionthat executes packet tunneling using the searched second interfaceinstead of the first interface.
 2. The mobile network control apparatusaccording to claim 1, wherein said search section comprises analternative router search section that searches for an alternativerouter apparatus which has a connection route to said global network andwhich belongs to said mobile network, and determines an ingressinterface having a connection route to the searched alternative routerapparatus out of interfaces provided for said router apparatus as thesecond interface.
 3. The mobile network control apparatus according toclaim 2, wherein said search section comprises a registration sectionthat registers a binding between an address of said ingress interfaceand an address of said router apparatus, and said alternative routersearch section searches for another alternative router apparatus whensaid registration section fails to register said binding.
 4. The mobilenetwork control apparatus according to claim 3, wherein saidregistration section acquires a global address from the searchedalternative router apparatus and registers a binding between theacquired global address and the address of said router apparatus when acurrent address of said ingress interface is not a global address. 5.The mobile network control apparatus according to claim 4, wherein saidalternative router search section searches for another alternativerouter when said registration section fails to acquire the globaladdress.
 6. The mobile network control apparatus according to claim 2,wherein said search section comprises an alternative interface searchsection that searches for an alternative egress interface which has aconnection route to said global network out of interfaces provided forsaid router apparatus, and determines said alternative egress interfaceas the second interface when the alternative egress interface issearched by said alternative interface search section, and saidalternative router search section searches for the alternative routerapparatus when the alternative egress interface is not searched by saidalternative interface search section.
 7. The mobile network controlapparatus according to claim 6, wherein said search section comprises aregistration section that registers a binding between an address of thesearched alternative egress interface and an address of said routerapparatus, and said alternative router search section searches foranother alternative egress interface when said registration sectionfails to register said binding.
 8. A mobile network control method,which maintains a connection that is constructed between a nodebelonging to a mobile network and a global network and is constructedthrough a router apparatus that has an interface having a connectionroute to said global network and belongs to said mobile network, themobile network control method comprising: a detection step of detectinga failure of packet tunneling executed using a first interface of saidrouter apparatus; a search step of searching for a second interface ofsaid router apparatus according to the failure of the packet tunnelingdetected in said detection step; and an execution step of executingpacket tunneling using the second interface searched in said search stepinstead of the first interface.